LT3 (FT3) | Free triiodothyronine

Free triiodothyronine (FT3/LT3) is a useful daily clinical diagnostic tool for the evaluation of thyroid status. The most important diagnostic application of FT3/LT3 is the diagnosis of triiodothyronine toxicosis. If FT4/LT4 is normal and TSH/TTH is decreased, FT3/LT3 should be tested. Elevated FT3/LT3 levels confirm triiodothyronine toxicosis (T3 toxicosis). FT3/LT3 testing is recommended if supraventricular tachycardia or proximal myopathy is detected without an increase in T4 concentration.

Immunological quantitative in vitro assay

Tested in blood serum